In the oil industry, shut-in tools are used downhole to provide downhole shut-in of the well so that various parameters of the downhole conditions such as pressure, temperature and flow from producing sections of the well can be measured more accurately. The shut-in tool is lowered into a gas or oil well with a slick-line truck and set and sealed with packing into a profile in the tubing in order that flow from the formation is directed through the shut-in tool.
A shut-in tool generally includes a valve system, a motor, a battery and microprocessor that enable the flow through the tool and hence, from the well, to be halted periodically such that downhole data from the producing zone can be measured and recorded. That is, the valve assembly is periodically closed thus sealing the producing zone from the surface in order that pressure and temperature profile of the producing zone can be recorded by recording sensors attached to the tool. After the desired amount of data has been collected, the valve assembly is opened and flow is again directed through the tool. The tool and recording sensors are periodically returned to the surface and the data is downloaded to allow engineers and geologists to both measure and predict the present and on-going production characteristics of the producing zone.
More specifically, in operation the valve is opened and closed by the motor in response to instructions from the microprocessor. The shut-in tool is normally programmed at the surface to set the desired open and close times for the valve, the specific times for opening and closing and the times between opening and closing depending on the specific information desired from the formation and the characteristics of the formation.
It is preferable that shut-in tools have fast reacting valves in order that the pressure readings immediately following valve closure are accurate. In the past, low closing valves (often requiring 2-3 minutes for closure) require that the data obtained be subjected to various mathematical compensation algorithms in order to compensate for the distortions in data during valve closure. While such algorithms may be partially effective in predicting instantaneous pressure build-up, these compensation techniques are subject to errors and, accordingly, there is a need for tools that have instantaneous or near-instantaneous valve closures in order that true instantaneous pressure data can be obtained.
Furthermore, as significant pressures may exist across the valve while the valve is closed (5000 psi), there is also a need for shut-in tools having an effective pressure equalization system that allows the pressure across the valve to be equalized prior to opening the valve.
It is also desirable that the tools have the necessary reliability and, in particular, be manufactured from abrasion resistant materials at the sealing surfaces to ensure effective sealing under abrasive conditions.
A review of the prior art reveals U.S. Pat. No. 5,332,035 U.S. Pat. No. 5,375,658, which describes a shut in tool having a piston.